sysmig: migration runner + initial 4 migrations (swap, daemon trims)

- up/down/status interface, history in /var/lib/sysmig/applied
- 001 swap 2GB + swappiness=10, 002-004 trim unneeded daemons (~56MB)
- google-osconfig-agent intentionally kept
- all messages/comments in ASCII English (console font safety)

migrations/004-purge-haveged.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+# 004-purge-haveged - Remove entropy daemon (~8MB)
+# Kernel 6.12 collects enough entropy on its own; haveged is redundant.
+set -euo pipefail
+
+export DEBIAN_FRONTEND=noninteractive
+
+case "${1:-}" in
+  up)   systemctl disable --now haveged.service 2>/dev/null || true
+        apt-get purge -y haveged >/dev/null
+        apt-get autoremove --purge -y >/dev/null
+        echo "    haveged stopped + package purged" ;;
+  down) apt-get update -qq
+        apt-get install -y haveged >/dev/null
+        systemctl enable --now haveged.service
+        echo "    haveged reinstalled + restarted" ;;
+esac